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Dec. 14, 2010 -- Forget Facebook, it's the thousands of close encounters within real, live social networks at high schools that could prove dangerous to students' health.

A new study shows that on a typical day high school students engage in thousands of social interactions that put them at risk for spreading disease and could spur a pandemic flu outbreak.

Researchers say any interaction between two people within 10 feet of each other has the potential to spread infections, such as influenza, common colds, and whooping cough, via droplets transmitted by sneezing, coughing, or direct contact.

The Spread of Flu

They recorded more than 762,000 such close encounters with the potential to spread disease on an average school day at a U.S. high school. Most of the interactions occurred within small social networks of students, and there were frequent repeated contacts within each group.

"Schools are particularly vulnerable to infectious disease spread because of the high frequency of close proximity interactions (CPIs) that most infectious disease transmission depends on," write researcher Marcel Salathe, of Stanford University, and colleagues in the Proceedings of the National Academy of Sciences. "Droplets from an infected person can reach a susceptible person in close proximity, typically a distance of less than 3 meters [about 10 feet], making CPIs highly relevant for disease spread."

In the study, researchers used wireless sensors on 788 people at the school, including students, teachers, and staff, to track their movement and contacts during a typical day in January. They then used a computer model to simulate the spread of a flu-like illness throughout the school.

Researchers say the results of the simulated flu pandemic fit well with the absentee records from the most recent flu season and suggest that social networks may be used to create more effective immunization strategies and prevent future flu pandemics.

SOURCES:Salathe, M. Proceedings of the National Academy of Sciences, Dec. 13, 2010, online early edition.News release, National Academy of Sciences.